The present invention relates to variable displacement compressors that control the inclination of a swash plate based on the difference between the pressure in a crank chamber and the pressure in cylinder bores. More particularly, the present invention pertains to a clutchless type variable displacement compressor.
Typically, vehicles have a variable displacement compressor used in an air conditioner. This and other auxiliary devices are actuated by the drive force of the vehicle engine through a drive train including a pulley and a V-belt. Some auxiliary devices, such as the variable displacement compressor, are not actuated all the time. It is therefore common to provide an electromagnetic clutch between the auxiliary device and the engine for selectively transmitting the drive force of the engine to the auxiliary device. For example, if provided between an engine and a compressor, the electromagnetic clutch selectively connects and disconnects the drive shaft of the compressor and the engine. However, if a compressor is directly coupled to a vehicle engine without an electromagnetic clutch, the shock caused by actuation and de-actuation of the clutch is reduced. This prevents passengers from feeling the shock and noise that are produced when the clutch connects or disconnects the compressor and the engine. Further, the clutchless construction reduces the weight and the manufacturing cost of the compressor. Thus, a clutchless type variable displacement compressor has been proposed.
Japanese Unexamined Patent Publication No. 8-159022 discloses such a clutchless type variable displacement compressor. The compressor includes a swash plate and a rotary shaft that tiltably supports the swash plate. The rotary shaft is directly coupled to a pulley without an electromagnetic clutch in between. A shutter chamber is defined at the center portion of a cylinder block extending along the axis of the rotary shaft. A suction passage is defined at the center portion of a rear housing, which is secured to the rear end of the cylinder block. The suction passage is aligned with the axis of the rotary shaft. A shutter, which has a large diameter portion and a small diameter portion, is slidably accommodated in the shutter chamber. The shutter selectively opens and closes the suction passage in accordance with the inclination of the swash plate. A coil spring is also accommodated in the shutter chamber. The coil spring urges the shutter in a direction opening the suction passage (that is, toward the swash plate).
The coil spring is located between the small diameter portion of the shutter and the inner wall of the shutter chamber, and extends between a step, which is defined by the large diameter portion and the small diameter portion, and a wall of the shutter chamber. When contracting or expanding in accordance with movement of the shutter, the coil spring slides along the inner wall of the shutter chamber and the small diameter portion of the shutter. The sliding of the coil spring prevents the shutter from moving smoothly thereby hindering accurate control of the displacement of the compressor. Further, sliding of the coil spring wears the coil spring and the parts contacting the coil spring. Therefore, there is a need to prevent the coil spring from sliding on other parts to improve compressor reliability.